One known way of improving tyre tread wear (i.e. to increase the rolling wear resistance of the tread and therefore the working life of the tyre) is to use special rubber compounds for the tread. Low-wear tread compounds, however, have the drawback of poor wet-road-holding performance (in other words, the improvement in wear achieved by altering the compound from which the tread is made is normally counterbalanced by a reduction in wet-road-holding performance).
Another known way of improving tyre tread wear is to reduce the voids in favour of solids in the tread pattern, to increase the rubber-on-pavement contact area of the footprint (and so reduce the specific pressure, and therefore mechanical stress, on the tread for a given vertical load on the tyre). This solution, however, further reduces wet-road-holding performance by impairing water purging from the footprint.
Another known way of improving tyre tread wear is to increase the footprint area (and so reduce the specific pressure, and therefore mechanical stress, on the tread for a given vertical load on the tyre). This solution, however, has the drawback of both reducing wet-road-holding performance and increasing rolling noise (i.e. the tyre is noisier).
A trade-off between the demands of wear resistance, wet-road-holding performance and rolling noise is therefore unavoidable, with the result that all three are good, but none is exceptional.
Patent Application EP878329A1 describes a tyre tread band comprising a centre; two shoulders on either side of the centre; and two edges on either side of the shoulders and forming a transition with the sidewalls.
In a first embodiment shown in FIG. 4B of Patent Application EP878329A1, the tread band profile comprises a first arc having a first radius R′; and two second arcs located outwards of the first arc and having a second radius Rs′ smaller than the first radius R′. At a junction, each second arc is connected continuously (i.e. with no discontinuity) to the first arc; and the radial distance To′, Tt′ between the extension of the first arc and the second arc increases gradually from the centre towards the shoulders.
In a second embodiment shown in FIG. 4C of Patent Application EP878329A1, the tread band profile comprises a first arc having a radius R′; and two second arcs located outwards of the first arc and having the same radius R′. At a junction, each second arc is connected discontinuously to the first arc, forming a step, wherein the second arc is not tangent to, and is radially lower than, the first arc; and the radial distance To′, Tt′ between the extension of the first arc and the second arc is constant from the centre towards the shoulders.